Chapter 8: Gene expression Flashcards
What is a genome?
All genetic material contained in an organism
What is a polypeptide?
A polymer of many amino acids linked by peptide bonds
What determines the amino acid assembled into polypeptides at ribosomes?
Nucleotide base pairs (A) adenine, (T) thymine, (C) cytosine and (G) guanine
How many base pair combinations make up an amino acid?
64 total combinations.
What is a codon?
A series of 3 nucleotide baes pairs in DNA and mRNA
Where are polypeptide instructions kept?
DNA
What makes polypeptides?
Ribosomes
What is messenger RNA (mRNA)?
Carries instructions out of the nucleus into the cytoplasm where ribosomes attach
How is mRNA generated?
Unwound DNA double helix
What is transcription?
First step in producing mRNA
What does RNA stand have that DNA doesn’t?
uracil (U) and pairs with A
What is the first step in transcription?
gene unwinds, then unzips exposing nucleotide bases
What is the other strand called that is not the template strand inn mRNA?
non-template or complementary strand
What joins RNA strand to template strand?
RNA polymerase enzyme
What happens after all nucleotide pairs are join in mRNA?
mRNA is released a single strand, the DNA zips up again and twist into double helix
What is pre-mRNA?
unmodified mRNA that contains introns (Still in nucleus )
Why are introns removed from mRNA?
They do not code for polypeptide production
What does allow for polypeptide production in mRNA?
exons
What is the process of removing introns and doing exons called?
Splicing
What occurs after splicing?
mRNA is mature and moves out of nucleus
What creates different types pf polypeptides?
Exons being spliced together differently
How does ribosomes start translating mRNA?
Once it reaches start codon
What is translation?
Joining of amino acids in specific order read from mRNA by ribosomes
What is tRNA?
A RNA molecule which picks up amino acids in cytoplasm which then carries them to specific mRNA for polypeptide synthesis.`
What shape is tRNA and why?
A clover shape to all anticodons to join nucleotide bases with mRNA
What is a anticodon?
A sequence of 3 nucleotide bases complementary to mRNA
Where do amino acids bind to tRNA?
Amino acid binding site opposite to anticodon
How does amino acids pass from tRNA to mRNA?
When anticodons bond to complementary on mRNA, the amino acids at the binding site are joined to chain of amino acids by peptide bond
When does ribosomes stop moving down mRNA?
When it comes to a stop codon
What happens to tRNA and mRNA?
tRNA is peeled off and goes and collects more amino acids and mRNA is broken down enabling the RNA to be used again.
What are the steps of mRNA?
DNA transcribed into mRNA modified into mature mRNA and is translated into proteins
What is coding DNA?
Small part of the DNA used as a template for mRNA (code for polypeptides, less than 2%)
What is non-coding DNA?
DNA not used for mRNA, 98% of DNA
What does non-coding DNA do?
Switches genes on and off (regulating genes that are active in cells)
What is a centromere?
Hold duplicated chromosomes (sister chromatids) together and are so the site at which spindle fibres move to chromosomes in cell division
What is a telomere?
Extension of DNA which prolongs the life of chromosomes
What is gene expression?
The process in which information is encoded in genes for polypeptides and thus protein synthesis
How is the process of gene expression regulated?
The process allows certain genes to be expressed in certain cells at required times and rates.
What are the factors that regulate the phenotypic expression of genes?
Chemical modification of chromatin at transcription stage; direct chemical modification of DNA at transcription stage; products of other genes at transcription; environmental factors; passed through offspring and translation stage
(Remember - proteins bindings to specific DNA (translation and transcription phase), products of other genes and environmental exposure)
How does chemical modification of chromatin at the transcription stage regulate phenotypic expression of genes?
When transcription occurs, DNA is wrapped very tightly and DNA polymerase cannot access the DNA and therefore the gene is switched off. Chemical modification (e.g. histone methylation) can unwrap the DNA causing the gene to be switched on.
How does the direct chemical modification of DNA at the transcription stage regulate phenotypic expression of genes?
methylation and acetylation to either disable or stimulate the transcription of DNA
How do the products of other genes at transcription regulate phenotypic expression of genes?
Activating proteins bind to non-coding DNA to unwind the histone proteins which allow the gene to be expressed.
How do environmental factors affect the phenotypic expression of genes?
Environmental factors the organism is exposed to after birth. Twins have the same genes yet can display different phenotypic expressions.
What are homeobox genes?
The genes responsible that regulate the body formation and patterning in developing an embryo. They are activated by specific concentrations of positional proteins e.g. Bicoid protein
What regulates differentiation for tissue formation and morphology?
Differential gene expression controlled by transcription factors
What is an example of a transcription factor that regulates morphology?
Homeobox genes e.g. fruit fly has 13000 genes but only 8 determine its morphology.
What is an example of a cell differentiation (determining of XY) that regulates morphology?
Need to know - (SRY Gene) is located on the arm of the Y chromosome. Once expressed, it produced testosterone influencing cellular development.
